1. Field of the Invention
This invention relates generally to an electronic gimbal system, and, more particularly, to an image stabilization electronic gimbal system for stabilizing an image from an imaging sensor.
2. Discussion of the Related Art
Target seeking imaging systems incorporating an imaging sensor to track a target of interest are known in the art. Inertial image stabilization is generally necessary for imaging sensors which are mounted on moving platforms, such as missiles or aircraft, to permit signal processing of the image data in a stabilized coordinate frame. Because the platform fluctuates due to vibrations caused by turbulence and the like as the missile or aircraft travels through the air, a scene sensed by the sensor as a frame of video data at one time may not be aligned with a consecutive frame of video data, thus causing significant distortion in the image. Therefore, by providing image stabilization the target of interest is more effectively tracked with higher image resolution.
Typically, inertial stabilization has been provided in the past exclusively by mechanical gimbals. A mechanical gimbal is generally comprised of one of a variety of different bearing structures which includes a torquing device for applying a torque to the sensor in a direction opposite to the vibrational disturbance, and thus, enable the sensor pointing direction to remain fixed as the platform vibrates around it. Generally, a separate gimbal is required for each of the roll, yaw and pitch axes in the inertial coordinant frame. As is known, stabilization in the roll direction of the platform is the most complex due to the requirements of slip rings and the like to provide for electrical connections from the sensor to the rest of the seeking system.
In one application, a requirement exists to roll an image for reasons other than inertial stabilization. One such application is in a helmet mounted display for an airborne infrared imaging system. Sensors mounted in an aircraft cockpit sense an operator's head motion such that the infrared imaging sensor is pointed in a direction corresponding to the head movement. Even in these miniaturized versions of imaging systems, a mechanical roll gimbal would ordinarily be required to roll the sensor as the operator's head is rolled from side to side.
As target seeking systems and the like incorporating imaging sensors have become physically smaller and/or have been designed with finer image resolution, the physical requirements on the mechanical gimbal stabilization systems have become much more complex and refined, and thus, more costly to produce. In fact, space requirements of some target seeking systems are beyond the present capabilities of providing a mechanical gimbal in the roll direction. Consequently, there is a need to address this problem.
Electronic image stabilizers have recently been introduced in the art of video cameras. In one particular implementation, a video camcorder has been incorporated with an automatic image stabilization system including a vibration type gyroscope sensor for providing image stabilization. See C. M. Oshima, et al., "VHS Camcorder with Electronic Image Stabilizer," IEEE Transactions on Consumer Electronics, November 1989, Vol. 35, No. 4. Although this system is apparently operable in the pitch and yaw directions, it is, however, not applicable to correct for disturbances in the roll direction. Furthermore, this system utilizes a method of altering the clocking sequence of the video data, thus making it necessary to have access to the timing signal of the detector. This, in effect, limits the ability to provide a remote camera.
What is needed then is a gimbal system which does not suffer the mechanical complexity and space requirements of the prior art gimbaling systems, and further, is operable in all three axes of pitch, roll and yaw. It is therefore an object of the present invention to provide such a gimbaling system.